LE 42LE5400 - no sound/picture

[jj14]

Hi,
I have a 42LE5400 that seemingly out of the blue, decided to stop working.

I was playing a game (console connected to HDMI 2), and the picture froze, then flickered, and the screen then went blank (all in a matter of about 20 seconds or so). While this was happening, I could hear a hissing sort of sound from the left side bottom of the screen (when facing the screen).

Rather than toss it away, I thought about trying to see if it could be fixed. I opened up the back panel, and tried the following steps after watching a video from shopjimmy https://www.youtube.com/watch?v=xUzCLgoSPGM

• The TV does power on (I can see the power button illuminate, and the light animation goes left to right across all other buttons)
• There is no picture on the screen (tried multiple inputs)
• There is no sound - I plugged in a chromecast to HDMI port and played music, and increased volume on TV - no sound
• I can't see any backlighting visible (even with the back cover off)
• Flashlight test doesn't show the menu (in a dark room, shone a flashlight on the screen after pressing "Menu" on remote)

See pictures of the back (click on the pictures to see higher resolution)

Any suggestions on how to proceed?
Thanks!

edit: uploaded pictures to this post

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

3rd picture (PSU) bottom left, there are some pin outs. Turn the TV on, measure the pin outs and post them here.

[jj14]

Re: LE 42LE5400 - no sound/picture

This is embarrassing - but what am I measuring? Assuming it is voltage measurement, which pins exactly am I measuring between? In the 3rd picture, bottom left, there are two sets of connectors (both with 1 set of blue wires, and 1 set of white wires) - are you asking me to measure voltage at two points on the connectors? or on the green PCB next to it?
(sorry, I'm not really familiar with this at all)

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

the 3rd connector (black) from the bottom has a cable going from the PSU to the main board. Next to the connector is a pin out, written on there what pin does what. We are going to need the pin out and the voltages you measure on each pin.
That's not going to be that easy, as everything has to stay connected. I have some special probes that have a small tip and I go behind the wire.
All measurements on that connector are Volts DC.

[jj14]

Re: LE 42LE5400 - no sound/picture

SIN ERROR      0(-0.5mV)
12V PDIM1      12.34V
12V SCLK       12.34V
12V DRV_ON      12.34V
GND VSYNC       0 (-0.3mV)
GND GND        0 (-0.3mV)
3.5V 3.5V       3.52V
3.5V 3.5V       3.52V
GND GND        0 (-0.1mV)
GND GND        0 (-0.1mV)
20V 20V       20.3V
PWR_ON 20V      3.38V

I double checked the last one (PWR_ON) - it is not 20V

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

that's only half of the pins. there are 2 rows!

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

-delete-

[jj14]

Re: LE 42LE5400 - no sound/picture

that's only half of the pins. there are 2 rows!

I see that - Doh!
I measured at the exposed pins on the black connector. I'll need to try to figure out where I can get at the remaining 12 pins (I don't see an obvious place to measure that on that connector). Will I need to remove the board to do that?


edit:

I have some special probes that have a small tip and I go behind the wire.
All measurements on that connector are Volts DC.

Oh, I see how you do that.. dang. I don't think my multimeter has these types of probes

[jj14]

Re: LE 42LE5400 - no sound/picture

Here are the voltages for all pins.
(Label1 Label2 Voltage 1 (for label1)---------Voltage 2(for label2)

SIN ERROR      0(-0.5mV) ---------0
12V PDIM1      12.34V   ---------2.9V
12V SCLK       12.34V   ---------0
12V DRV_ON      12.34V   ---------0
GND VSYNC       0 (-0.3mV) ---------0
GND GND        0 (-0.3mV) ---------0
3.5V 3.5V       3.52V   ---------3.52V
3.5V 3.5V       3.52V   ---------3.52V
GND GND        0 (-0.1mV) ---------0
GND GND        0 (-0.1mV) ---------0
20V 20V       20.3V   ---------20.3V
PWR_ON 20V      3.38V   ---------20.6V

[budm]

Re: LE 42LE5400 - no sound/picture

DRV_ON = 0V = No backlights, you do not have BL-ON signal.

[jj14]

Re: LE 42LE5400 - no sound/picture

Thank you. I assume that doesn't necessarily mean that the backlight is bad, but rather that that Backlight is not being triggered for some reason.

Is this something that a relatively inexperienced person like me can fix?

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

I am afraid you need a new main board.

[jj14]

Re: LE 42LE5400 - no sound/picture

bummer.. I looked at shopjimmy, and looks like they don't have these in stock
I'll look around on other sites, but is a mainboard replacement easy to do? (assuming it is affordable)

Also, mainboard - that's the one with the input ports, right? Given that the signal was the problem (on the power supply board), would that not be the issue? (not questioning your diagnosis - just trying to understand)

Thank you & budm for helping with this.

[CapLeaker]

Re: LE 42LE5400 - no sound/picture

Easy. The PSU has always STBY voltage on. That goes to the main board. You press the "On" button, the main board will send PSon and BLon back to the PSU. The PSU in return will turn on all the voltage rails and the back light, the TV is on. Without the mainboard commanding the PSU on, the PSU stays off unless you force it on. A bad main board is a bad main board. Unless you have a hot air rework station, knowledge and the parts, there is no go to fix the main board. So it has to be a replacement board.

[jj14]

Re: LE 42LE5400 - no sound/picture

Thank you CapLeaker
I am certainly not going to attempt to fix the board. I'll keep searching for the replacement board.

Thanks again for your patience

[budm]

Re: LE 42LE5400 - no sound/picture

You can force on the backlights to see if they will come on just in case you have more than just main board problem.

[jj14]

Re: LE 42LE5400 - no sound/picture

How do I do that? (that's a great suggestion)

[budm]

Re: LE 42LE5400 - no sound/picture

You need to disconnect just the DRV_ON wire that goes back to the main board first, then use 1K 1/4W (or larger will be fine) resistor between the standby (3.5V) power supply pin and the DRV_ON pin of the power supply, plug the TV into the outlet and turn on the TV to see if you will get backlights.

[jj14]

Re: LE 42LE5400 - no sound/picture

Thank you
I'll look for the resistor

One more question though - is there an easy way to disconnect just the DRV_ON wire (given that is it part of the 24 pin connector)

[budm]

Re: LE 42LE5400 - no sound/picture

Thank you
I'll look for the resistor

One more question though - is there an easy way to disconnect just the DRV_ON wire (given that is it part of the 24 pin connector)

That female connector is hard to remove the pin from the housing, You can try removing the pin on the end that goes to the main board instead, or you can cut the wire and splice it back together later on.
BTW, the resistor can be as low as 470 Ohms or anything between 470~1000 Ohms.